Acute megakaryoblastic leukemia (AMKL) is a subtype of acute myeloid leukemia characterized by increased megakaryoblasts in the fetal liver and/or bone marrow. The leukemia usually presents in infants, and has a very poor prognosis. One of the main cytogenetic abnormalities associated with AMKL is a translocation between chromosomes 1 and 22, resulting in the fusion protein, OTT-MKL1 (OM). In our laboratory, we discovered that OTT and MKL1 are differentially regulated in normal megakaryopoiesis as OTT expression is downregulated whereas MKL1 expression is upregulated during the differentiation, and we have begun to elucidate the functions of OTT and MKL1. However, the molecular function of OM in megakaryocyte differentiation and/or in leukemogenesis is largely unknown. We have observed a rapid induction of cell death upon OM expression in various cell lines and primary cells. Furthermore, in a previously published mouse model expressing the OM fusion transgene, development of AMKL in these mice is slow and rare. These results suggest that OM induced leukemia is a multistep process that requires acquisition of additional mutations in cancer cells for survival of the initial cell death induced by OM and for subsequent proliferation. Therefore, I hypothesize that additional collaborating genomic lesions promote OM- induced AMKL and these mutations define a network of factors that promote AMKL. I propose to elucidate the mechanisms by which OM disrupts normal megakaryocytic differentiation and induces leukemia. I will identify potential OM-collaborating mutations based on deep sequencing data from an AMKL patient sample and validate these mutations using primary murine and human hematopoietic cells with engineered inducible OM transgene expression. I will complement my mutation analysis using shRNA and small molecule screening approaches to functionally define genes and signal networks affect by the OM fusion gene. These studies will provide critical molecular details of OM and its leukemogenic role in AMKL to understand the disease and for development of targeted therapies for this disease. ) PUBLIC HEALTH RELEVANCE: Chromosome translocation is a common structural abnormality in cancer cells that results from joining of two separate chromosomes at a specific breakpoint to generate a fusion gene whose product promotes oncogenesis. Acute megakaryoblastic leukemia is associated with a recurrent translocation that results in a fusion protein. My project aims to determine molecular mechanisms responsible for the fusion protein to induce acute megakaryoblastic leukemia. )